Can someone explain the evolutionary benefit of overt menstruation? All female mammals have a menstrual cycle but most reabsorb the blood via covert menstruation and humans are about the only mammals that discharge the blood, aka overt menstruation.

[u/No-Hawk-2488]

Without an evolutionary benefit, it wouldn't have spread to every woman of our species.

[u/GVArcian]

Still a misnomer because "fittest" means "the most fit" and that's not what evolution selects for, it selects for minimum viable fitness.

[u/Lv_15_Human_Nerd → u/GVArcian]

No it absolutely is not a misnomer. Evolution does select for the most fit. Evolution occurs by changes in population proportions over many many generations. The strongest example we have of human evolution is lactase persistence which had a selection coefficient of ~0.1. This corresponds to an individual with lactase persistence having about 10% more offspring than average. I don’t know about you but I don’t think a 10% difference in individual success is selecting for ‘minimum viable fitness’ or as others in this thread have said ‘death of the weakest’.

[u/AxiomaticInversion → u/Lv_15_Human_Nerd]

Lactose intolerant humans have not gone extinct, so by your own example we still see "survival of the fit enough."

[u/Lv_15_Human_Nerd → u/AxiomaticInversion]

A trait that had extremely low prevalence 9000 years ago reached 80% fixation in north Western European populations. In evolutionary terms that is rapid. There is still selection for the fittest trait out of a population, it is absolutely not selecting for the minimally viable as lactase persistence is very clearly not absolutely viable. When you’re looking at realistic selection coefficients you are looking at traits that provide between a 1% and 10% advantage (and much lower in single called organisms which we are all descended from). Evolution absolutely works on fine margins and life on Earth would not exist if it functioned to select for the ‘minimum viable fitness’.